The present invention pertains to hydraulic jack systems used in felling trees and an improved safety check valve having application to such systems.
It has been a practice in the prior art to employ hydraulic jacks in a backcut of a tree to assist in felling the tree in a desired direction. Those skilled in the art will appreciate that such hydraulic jacks many times provide the only practical technique for felling a tree in a desired direction, particularly when the tree is leaning away from the desired direction. Hydraulic jack systems employed in the prior art have heretofore not provided a convenient method for adding hydraulic jacks as needed to the system while one or more previously activated jacks remain in load supporting relationship in the backcut of a tree. Furthermore, such systems have either been characterized by inadequate safety provisions or failed to provide an efficient means for collapsing the jacks after the tree has been felled.
In one such prior art system, each jack is isolated from the remaining portions of the hydraulic network by means of a check valve which is shunted by a manually operable needle valve. When the needle valve is closed, the check valve is operable to permit the jack to be pumped up to its peak working pressure and maintained at such pressure to continue supporting the load of a tree in the event of a loss of pressure on the pump side of the valve. Once the tree has been felled, the jack can be collapsed by merely opening the needle valve to drain the hydraulic fluid from the jack around the check valve.
One disadvantage with such a prior art system is the likelihood of accidentally opening the needle valve while a tree is being supported by a jack thus causing the jack to collapse and the tree to fall backward in the wrong direction with consequent injuries and property damage. Accordingly, it would be desirable to provide a tree-felling system in which it is not possible to inadvertently bypass a safety check valve while the hydraulic jack is in load supporting relationship with the tree.
Another disadvantage with such a prior art system is that needle valves are relatively time consuming devices to operate in that they require at least several complete turns in order to open the valve fully from a closed position. Accordingly, it would be desirable to provide a more efficient mechanism for quickly collapsing the jacks in a treefelling system after the tree has been felled.